24v bank 4p2s
- Thread starter Miyaksue
- Start date
sunshine_eggo
Victron's little biatch
But 4P2S implies you want 24V (25.6V). What gives?
If so, you want 2S4P - 4 strings of two 12.8V in series in parallel...
4P2S means you wire 4 in parallel and another 4 in parallel and then series those two groups. You don't want to do that because you lose site of 100% of the battery voltages. When you go 2S4P, you can measure the individual 12.8V batteries.
Better yet, 24V batteries in parallel are even better.
Feels like there's not enough info.
Depends on the max load, system voltage, and wire rating.
sunshine_eggo
Victron's little biatch
How do you plan to run a 12V A/C unit off 24V? Is this an inverter-type A/C?
P and S indicate parallel and serial. The order stated are the order they are connected.
Four batteries in parallel have ONE voltage no matter which battery you measure. You can't tell if any are in protection mode and disconnected from the circuit.
Two batteries in series allow you to measure each individual 12V. Taking multiple 2S strings and paralleling them at the ends means you can measure each individual 12V and determine if there's an issue.
sunshine_eggo
Victron's little biatch
Yes, but I would be concerned about the cost of a 850W / 12V / .8 = 89A 24V-12V converter.
Do you already have the 12V A/C? IMHO, the cost associated with DC appliances is rarely worth the small efficiency savings vs. AC powered appliances.
The only converter I'm even the least bit familiar with that will work is the Victron Orion 24/12-70. To power your A/C unit you would need two of these converters.
HarryN
Solar Wizard
This DC - DC converter can support up to 60 amps.
These guys make really rugged products, so they tend to be a bit more expensive. No tariffs since made in USA.
These guys make really rugged products, so they tend to be a bit more expensive. No tariffs since made in USA.
Model 384 | SEC America
22v-60v to 12v High Power DC-DC Converter INPUT VDC 22 - 60 OUTPUT VDC (NOMINAL) 13 OUTPUT ADC 60 Read more Model 384 ›
www.secamerica.com
This DC - DC converter can support up to 60 amps.
These guys make really rugged products, so they tend to be a bit more expensive. No tariffs since made in USA.
Model 384 | SEC America
22v-60v to 12v High Power DC-DC Converter INPUT VDC 22 - 60 OUTPUT VDC (NOMINAL) 13 OUTPUT ADC 60 Read more Model 384 ›www.secamerica.com
Pretty good specs!
HarryN
Solar Wizard
The normal way to do this would be to build a 12 volt pack for the air conditioner, and a 24 volt pack for everything else.
Connect them together with a DC - DC charger.
The 12 volt pack can be fairly modest - just 2 batteries to deal with the surge.
Connect them together with a DC - DC charger.
The 12 volt pack can be fairly modest - just 2 batteries to deal with the surge.
HarryN
Solar Wizard
Yes - and I have direct experience with them in mobile applications.
They originally were focused on the mil / telecom market, but have expanded over time.
You can put their stuff on a telephone pole in the middle of Alaska and not worry. ( the sealed units )
Interesting..
the reason I’m considering a 24v bank is that I have the batteries already which you can max array as 4s4p.
That will work. I haven't seen anyone on the forum use that one so I can't point you at any posts for a review.
HarryN
Solar Wizard
Interesting..
Normally, you start by looking at your largest load ( in terms of power draw ) and that sets the tone for the rest of the power system.
If you had a 120 vac powered air conditioner, then this is the load that needs the most attention - and would drive decisions about the inverter, battery pack configuration, etc. Going from 12 volt --- 24 volt improves the inverter efficiency, and the wire sizes are significantly smaller, so it makes sense to do that change for an inverter ( 2 - 3 K watts ).
24 volt is also handy, because it is almost perfect for powering modern USB ports, even better than 48 volt in many cases, and there are water pumps, fans, etc available.
Also using 24 volts, allows for double the solar charge rate ( power ) using the same equipment, as it is "amps based" and does not care if your battery is 12 vs 24.
_________-
So if you were starting from scratch, buying a 24 volt vs a 12 volt air conditioner would be a much easier path. If it is easy to return it and buy a 24 volt version, then this will make your life easier, but it might not be possible.
If not, then you need to decide if your inverter will be powering more things or your air conditioner. If the other inverter use is not all that much compared to the a/c, then it might even make sense to just keep everything at 12 volt - in spite of how much I don't want to say that.
I appreciate all the help.
The 12v 850w AC is the main and largest load.
The other component we are also set on are the 8 100ah lifepo batteries. Those could make a 24v bank or 2 x 12v banks connected thru a dc/dc?
If I go for a 24v battery bank, what ga wire do I use to connect them batteries?
HarryN
Solar Wizard
There are various approaches to wiring battery packs together.
The main considerations are
- Sometimes the battery bms will trip, and this requires the battery to be disconnected from the rest to re-set
- Safety - as in having things like fuses or breakers, the correct wire size, etc - and doing it in a way that you can actually buy the parts
- Battery terminal heating. You don't want all of the power from all of the batteries to be flowing through an individual terminal
- Charging / discharging reasonably evenly
- Maintenance and changes
This is the approach that I like to use. It puts each parallel string of batteries on it's own breaker, and uses a bus bar as the common power distribution point. It shows just one battery in each string, but I routinely use it as well for 24 volt systems with 2 batteries in series.
It is one of many ways to do it, but I like it for my own use.
Basically the batteries are on the left side of the diagram, and the loads / charging are on the right side.
It can be built using 2 awg wire ( good for 100 amps per feed ) and you can use a breaker up to 125 amps on each one.
Take a look at your batteries and see if 100 amps of discharge is appropriate for them.
This just shows 2 strings of batteries in parallel, but you can add as many as are needed - with your size system.
The DC - DC converter can be attached for example where a fuse block is shown.
The dual feed to the inverter is for use in 12 volt systems, for example if you were trying to feed 12 volts into a 2 000 watt inverter, it takes ~ 200 amps. With 24 volt, it only needs 100 amps, so it works just fine to use 1 string to feed it.
Some people like to add a battery terminal fuse to each battery "string" to provide cut off at that point as an additional safety measure.
What I really like about the concept is that it allows shutting off various portions of the system for testing or isolating things off in case they are not working correctly.
In theory you can just use a fuse instead of the breakers, but then imagine having the power of so many batteries feeding your system, and no way to really turn if off to hook something up or make changes ? This kind of arrangement is even fairly safe for teenagers to use.
________________
For the 12 volt air conditioner, 2 awg should also be very close to the requirement. On the blue sea web site, there is a calculator that you can use to double check.
Circuit Wizard - Blue Sea Systems
circuitwizard.bluesea.com
2 awg wire is fairly easy to work with and widely available. You can just order on line the wires with terminals crimped on already - usually cheaper than you can buy the parts.
edit - that DC converter might be limited to 6 awg wire - cannot remember right now. It is in the data sheet / manual.
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I'll probably get shot down by people that obsess over slight differences in charge states and battery wear for saying this, but, even if the battery manufacturer says 4P max, I don't really see an issue with going higher than that in parallel. In series, going more than 4 is a bad idea, but in parallel, as long as you're not trying to push some extreme amperage, you start off well balanced, and have everything properly fused, why not just go 8P 12V and keep it simple?
HarryN
Solar Wizard
You can, as long as you aren't just passing all of the current point to point through the batteries.
The terminals toward the ends will get hot and can internally damage the battery.
Also you need a way to turn off each battery, so it just takes more breakers and a longer bus bar.
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